1. Field of the Invention
The present invention relates to a process for producing a styrenic polymer. More particularly, it pertains to a process for producing a styrenic polymer having a high degree of syndiotactic configuration efficiently and inexpensively.
2. Description of the Related Arts
In recent years, a process for producing a styrenic polymer having a syndiotactic configuration (hereinafter sometimes referred to as "SPS") by polymerizing a styrenic monomer by means of a catalyst comprising a transition metal compound as a primary ingredient, especially a titanium compound and methylaluminoxane (refer to Japanese Patent Application Laid-Open No. 187708/1987) has been proposed.
There has also been proposed a process for efficiently producing such a styrenic polymer (SPS) by the use of a catalyst comprising a coordination complex compound composed of an anion in which a plurality of radicals are bonded to a metal and a cation, while dispensing with an aluminoxane which is expensive and is to be used in a large amount (refer to Japanese Patent Application Laid-Open Nos. 415573/1990, 415574/1990, etc.)
In the case of polymerizing a styrenic monomer by the use of the above-mentioned catalyst, there has heretofore been employed an alkylaluminum as a chain transfer agent for the purpose of modifying the molecular weight of the objective polymer. However, this method involves the problems that the catalytic activity deteriorates resulting in an increase in the amounts of residual metals contained in the styrenic polymer thus produced, allowing the decomposed product of an alkylaluminum to remain in the objective polymer. Even in the case of raising the polymerization temperature, the deterioration of the catalytic activity increases the amount of residual metals in the objective polymer. The aforesaid situation calls for the development of a process capable of producing a styrenic polymer of high performance at a low cost, while enabling a decrease in the molecular weight of the resultant polymer and simplifying the process itself without deteriorating the catalytic activity.
As a result of intensive research and investigation made by the present inventors under such circumstances, it has been found that in the case of polymerizing a styrenic monomer by the use of a transition metal compound, a coordination complex compound composed of an anion in which a plurality of radicals are bonded to a metal and a cation, or methylaluminoxane, and an alkylating agent as principal components, the use of a reaction product between a straight-chain alkylaluminum having at least two carbon atoms and water can lower the molecular weight of the resultant polymer without deteriorating the catalytic activity. The present invention has been accomplished on the basis of the above-mentioned finding and information.